Hitherto, various attempts have been made to utilize the solar light energy reaching the earth's surface. However, most of the prior art solar energy systems involve the conversion of the captured solar light energy into electric or thermal energy and, as far as I am aware there are very few that directly utilize the solar beams themselves as a source of optical energy. In lighting applications, it is obvious that the use of solar energy in the form of optical energy is advantageous since conversion loss is obviated.
With a view to providing a solar system which employs solar radiation as a light source, I have previously developed an apparatus for collecting solar beams capable of condensing the solar beams so that they are introduced into an optical conductor, such as an optical fiber (Japanese Patent Laid-Open Publication No. 55-28055). Being reflected at the boundary surface of the optical fiber, the light rays or solar beams propagate therealong and then issue out of the optical fiber from its exit end. The angle of emission of the light rays issuing from the exit end of the optical fiber depends on the critical angle of incidence of the material forming the optical fiber and, normally, is usually not greater than about 48.degree. for an optical fiber made from pure silicate. When the interior of a room is illuminated with light rays issuing from one or a bundle of optical fibers, illumination takes place in a spotlight-like fashion. Thus, it is not possible to illuminate a sufficiently wide area with soft or mellow light rays.